Steve,
Thanks for the info!
This should be an interesting adventure!
Thanks & 73,
Gordon Beattie, W2TTT
201.314.6964
-----Original Message-----
From: towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com] On Behalf Of Steve Hunt
Sent: Monday, September 08, 2008 8:38 AM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] TH6DXX at various heights
Gordon,
There's a couple of pages of information about antenna height on my web
site that you might find interesting, particularly the second page. They
are part of the Hexbeam section, but the data applies equally to any
beam. The conclusions were:
"For those of us constrained to use a single multiband antenna mounted
at a fixed and modest height, the results offer some encouragement: if
we can get the antenna up around the 40ft-50ft mark we will be within
1dB of the optimum height for short-haul and medium-haul paths on all
bands 20m thru 10m. And we will probably accept the "half S point"
penalty that our modest height suffers on the long-haul paths.
If our antenna is presently at the 20ft mark, the effort and expense
required to lift it to around 40ft looks well worthwhile; we will see
improvements ranging from 1dB to 5dB, depending on the path and the band.
For the "serious" operator who is able to justify the expense and
engineering challenges of lifting the antenna to 80ft or more, the
results show that significant benefits will accrue on the long-haul
paths; but the ability to switch to a lower antenna under certain
propagation conditions becomes increasingly important, particularly at
the highest frequencies.
Finally, a note of caution! The HFOM involves a weighting factor based
on arrival-angle statistics. This means that, even though we may have a
good /average/ HFOM, there may still be times when the antenna performs
poorly. For example, the Hexbeam at 80ft produces a reasonable HFOM of
8dBi on 20m short-haul paths. However, if at some particular instant the
signals are arriving in the range 22° to 26° (which they will do over
25% of the time), we will wish we had another antenna at a different
height we could switch to!"
For more details, including an explanation of what I mean by HFOM, see:
http://www.karinya.net/g3txq/hexbeam/height/
http://www.karinya.net/g3txq/hexbeam/height_2/
73,
Steve G3TXQ
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